The Preparation And Modification Of Silicon-based Anode Materials For Lithium-ion Batteries

With the rapid development of electronic equipment and electric vehicle,the demand for rechargeable battery is becoming more and more serious.The pursuit of high capacity,excellent rate performance and stable cycle performance of rechargeable battery is the current research hotspot.Due to the highest theoretical specific capacity of 4200 mAh g-1,stable charging platform,high safety,non-toxicity,and abundant reserves,silicon material has been considered as a promising anode material for next-generation lithium-ion battery.However,silicon,as a negative electrode material for lithium ion batteries,has a huge volume effect and low self-conductivity,which limits its commercial application.Therefore,different types of synthetic methods have been efficiently used to prepare nanoscale silicon materials,nano-Si@carbon composites and the modification of silicon oxide material in this paper.The above materials were detected by means of XRD,SEM,TEM,BET and other characterization methods as well as various electrochemical performance test methods.The nano-Si material is successfully prepared by a simple magnesiothermic reduction process.The microstructure and electrochemical performance test results of the nano-Si prepared under the two conditions were compared.It can be concluded that the SC-Si material prepared by adding sodium chloride as a heat-scavenger during the experiment shows better electrochemical performance.The SC-Si electrode displays an initial charge specific capacity of 1875 mAh g-1,with the first coulomb efficiency of 85%.The specific charge capacity can still maintain 1007 mAh g-1 after 50 cycles under a current density of 600 mA g-1.The charge specific capacities at the current densities of 100 mA g-1,400 mA g-1,800 mA g-1 and 1200 mA g-1 are 1983 mAh g-1,1650 mAh g-1,1017 mAh g-1,and 675 mAh g-1 respectively.The excellent electrochemical performance of the SC-Si material is mainly attributed to the large amount of heat generated by sodium chloride consumed in the process of magnesiothermic reduction.The smaller silicon grains are obtained,and the transmission path of lithium ion is effectively shortened,thus the utilization of nano-Si particles can be improved.The metathes reaction is applied to synthesize the nano-Si@C composite materials in the bamboo charcoal matrix using bamboo crumbs as carbon sources.The structural characterization and electrochemical performance of co:mposite materials are tested to determine the best preparation conditions:the carbonization temperature of bamboo chips is 900 ?,the temperature of zinc immersion is 600 ?,and the mass ratio of zinc to bamboo charcoal is 2.5:1.The initial charge specific capacity of nano-Si@C composite materials is 757 mAh g-1,and the initial coulomb efficiency is 73%.The capacity retention rate of nano-Si@C composite materials is 74%after 50 cycles with a current density of 600 mA g-1,and the coulomb efficiency is kept in the range of 98-100%during the cycle process,exhibiting good cycle stability and reversibility.However,nano-Si material has a capacity retention rate of 36%after 10 cycles at a current density of 200 mA g-1.It can be seen that carbon coating on nano-Si can significantly improve its cycling stability.Using a simple and effective high-temperature immobile phase method,ZnO is used to convert some active oxygen from the SiO material to an inert Zn2SiO4 material.Through the structural characterization and electrochemical performance tests of the modified SiO material,the analysis results show that the optimal preparation conditions are as follows:the reaction temperature is 800 oC,and the molar ratio of SiO to ZnO is 7:1.The initial charge specific capacity of the modified SiO material increased from 869 mAh g-1 to 1030 mAh g-1,and the initial coulomb efficiency increased from 59%to 67%.The capacity retention rate of the modified SiO material is increased from 65%to 74%after 50 cycles.It can be seen that ZnO modification not only improves the initial reversible capacity and initial coulomb efficiency of SiO materials,but also improves its cyclic stability performance.